Blood coagulation tests are carried out in order to recognize the pathology of a blood coagulation fibrinolysis system, to diagnose a disseminated intravascular coagulation syndrome (DIC), to confirm a thrombus treatment effect, and to diagnose hemophilia. In particular, as for blood coagulation time measurement, a time until a fibrin clot is formed after a specimen and a reagent are mixed with each other (hereinafter, referred to as a blood coagulation time) is measured. In a case where there is a congenital or acquired abnormality, the blood coagulation time is prolonged.
However, if the blood coagulation time is merely measured, it is not possible to determine whether the cause of the abnormality is activity degradation resulting from blood coagulation factor deficiency (deficiency type), or whether the cause of the abnormality is activity degradation resulting from blood coagulation reaction inhibition (inhibitor type) of an antibody with respect to a component configuring a blood coagulation system or a component in a blood coagulation time measurement reagent.
On the other hand, in a case of treatment, it is necessary to clarify the cause of the abnormality, since a treatment policy varies depending on whether the cause of the prolonged blood coagulation time is the deficiency type or the inhibitor type.
As a method for determining the cause of the prolonged blood coagulation time, there is a cross mixing test (also called a blood coagulation correction test or a cross-flow-over test) using added normal blood plasma. In the cross mixing test, the normal blood plasma is added to subject blood plasma, and a correction degree of the blood coagulation time is graphed and determined. As the most representative application example of the cross mixing test, a factor of prolonged APTT is determined. However, in some cases, items such as prothrombin time (PT), dilute PT (dPT), dilute APTT (dAPTT), kaolin coagulation time (KCT), and dilute Russell's viper venom time (dRVVT) are performed.
Incidentally, although APTT is a major item that can be performed in most facilities for carrying out the blood coagulation tests, a current situation hardly shows that the cross mixing test is frequently carried out. In a case where APTT cannot be performed in the facilities and an outsourcer is requested to carry out the test, it takes time to receive results, thereby leading to delayed discovery and delayed treatment start of severe diseases such as haemophilia. The reason why this situation occurs is that preparation and incubation work of a specimen is complicated and interpretation of the result is not clear. Consequently, the work requires a tester's skill job.
In order to solve the above-described problem, PTL 1 proposes the following technique. According to PTL 1, each blood coagulation time is measured for subject blood plasma alone, normal blood plasma alone, and a sample (mixed blood plasma) obtained by mixing the subject blood plasma and the normal blood plasma at least at one mixing ratio. A difference is obtained between a lower area (A) of a line graph in which an obtained measured value is plotted and a lower area (B) of a straight line connecting measured values of the subject blood plasma alone and the normal blood plasma alone. An area ratio (A−B)/(B) of the difference is compared with a predetermined reference area ratio Y. Based on the comparison result, it is determined whether the cause is the inhibitor type or the deficiency type.